The present invention relates to a fixing device with pulling rollers for use in image forming apparatuses, such as electronic photographing machines.
Conventionally, images for transparent sheets for use in an overhead projector (OHP) have been chiefly formed by printing or hand writing. Recently, they are often made in an image copying process as electronic photographing copying machines have been made popular.
What is more, those images have been conventionally monochrome ones, but color images have been mainly duplicated as color image forming apparatuses were developed. This allows the OHP to project drawings, graphics, photographs, and the like at a high projection effect.
However, the prior color image forming apparatuses having a fixing device fix a color toner image transferred to a transparent sheet. In this event, a leading part of the sheet can be separated from the heating roller relatively easily, but the following parts are often made too late in separation timing as-they are likely adhered to a surface of the heating roller. This causes the fixed image to lose gloss, resulting in mat image. This tendency occurs, particularly in image transference on the entire sheet.
The color image projected is worse in the color saturation and greatly inferior to the monochrome image in the clearness as the color image formed on the sheet is degraded in the transparency.
In order to correct such a decrease of the separatability of the local parts of the transparent sheet from the heating roller, it was proposed to provide a guide member for changing down a conveying direction of the sheet right behind the heating roller. The proposal has not been employed as the guide member deteriorates the image quality as it has the image surface Just fixed slid thereon.
In view of such a problem as pointed above, it is an object of the present invention to provide a fixing device that increases separatability of a transparent sheet from a heating roller and with this, is capable of fixing highly transparent color images and glossy color images even on ordinary transfer-media.